Fluid compression rolled (FCR) polymeric films are disclosed in Williams, Jr., et al. U.S. Pat. No. 3,504,075; such films exhibit a most advantageous combination of properties, including clarity, tensile strength, moisture barrier characteristics, etc. While the disclosure of that patent is hereby incorporated by reference hereinto, it might be pointed out it teaches a technique for cold rolling a polymeric sheet or film to effect a substantial thickness reduction wherein a lubricant is utilized to produce a hydrodynamic wedge in the nips between the rollers and the polymeric web. This produces molecular orientation of the polymer in the machine (longitudinal) direction which, in turn, is responsible for at least some of the outstanding properties exhibited by the film.
Although such films are highly desirable for many uses, certain characteristics which they possess, and which are attendant to the linearity produced by compression rolling, render them impractical, or at least somewhat undesirable, for some packaging applications. More specifically, the high clarity and low moisture vapor transmission rates (MVTR) which typify these films make them uniquely suited for the packaging of moisture-sensitive comsumer items, such as pharmaceuticals (e.g., pills, capsules, and the like). Those items are desirably sold in strip packages, in which each pill is individually encased within a pocket or cell formed by producing a series of lateral and transverse seals (normally heat seals) along the length and across the width of two coextensive films.
While such oriented films are generally heat sealable, the tendency for deorientation to occur at elevated temperatures, on the one hand, coupled with the necessity for achieving certain minimum sealing temperatures, on the other, often confine operating temperatures to a range which is too narrow for practical purposes (e.g., 15 Fahrenheit degrees). Thus, the dimensional changes which occur upon excessive deorientation at overly elevated temperatures will so stress and distort the seal areas as to make the bond strength attained inadequate, at best; the same result will occur if insufficient heat is provided at the seal areas for adequate fusion.
A second source of difficulty resides in the weakening that is induced in the cross-machine direction of the film (i.e., the direction transverse to the axis of orientation), which tends to cause splitting, especially adjacent the longitudinally extending lateral seal areas. Loss of integrity of the package is, of course, intolerable, and the problem is particularly troublesome when the item packaged is large relative to the size of its cell, due to the stresses which are thereby produced.
Finally, whereas it is typically quite easy to tear a compression rolled film in the machine direction, the same molecular orientation which is responsible for that effect also produces a commensurate resistance to tearing in the transverse direction. Hence, when such films are used for strip packages, the practical consequences are that the cells may be separated from one another or opened manually in one direction, but not in the other. This factor is, of course, of primary importance to such an application, since the inability to easily tear one unit from the remainder of the strip would virtually preclude consumer acceptance of such a package.
Accordingly, it is a primary object of the present invention to provide a novel film, which exhibits desirable moisture barrier, heat sealing and biaxial tearing characteristics, coupled with such levels of tensile strength and elongation as will prevent undue splitting of the web and will permit its use in connection with conventional packaging machinery.
More specific objects are to provide a film which is adapted for use in the fabrication of strip packages, to provide such packages, and to provide methods by which such a film and such a package may be produced.